Printed circuit boards usually have interfaces supporting different kinds of storage devices and peripheral cards. For example, Socket2 is one kind of interface produced by INTEL for different kinds of devices. A +3.3 volts auxiliary voltage provides power supply for the Socket2 interface. When a wireless wide area network (WWAN) device is inserted in the Socket2 interface, the +3.3 volts auxiliary voltage provides power supply for the Socket2 interface in either working state or sleep state. When a solid state disk (SSD) device is inserted in the Socket2 interface, the SSD device only needs the power supply when in a working state.